The disclosure relates generally to combined cycle power plant system, and more particularly, to bypass conduits for reducing fatigue and stress experienced by components within a heat recovery steam generator (HRSG) of the combined cycle power plant system.
Power systems typically include a variety of different turbomachines and/or systems that are used to generate operational load and/or power output. Two conventional power systems used to generate operational loads include gas turbine systems and combined cycle power plants, which typically include a gas turbine system(s). Conventional combined cycle power plants employ one or multiple gas turbine system(s) operatively coupled to one or multiple steam turbine system(s). The gas turbine system includes a compressor coupled to a gas turbine. The gas turbine is usually coupled to and drives an external component, such as a generator, for producing a load or power output. The steam turbine system includes a high pressure (HP) turbine portion operatively coupled to an intermediate pressure (IP) turbine portion that, in turn, is coupled to a low pressure (LP) turbine. Similar to the gas turbine of the gas turbine system, the HP, IP and LP turbines are employed to drive an external component (e.g., generator). In a typical combined cycle power plant, exhaust gas from the gas turbine is passed to a heat recovery steam generator (HRSG), which may be used to reheat and provide steam to the various turbines of the steam turbine system for enhanced efficiency of the system and/or power plant. Downstream of the HRSG the exhaust gas is released to the atmosphere through a stack.
However, during operation of the power system, portions and/or components may experience high stress and thermal fatigue due to rapid temperature change of the components. For example, when the power system undergoes a start-up procedure, the HRSG may immediately begin to generate high temperature steam. This high temperature steam may be provided, supplied and/or moved through portions and/or various components (e.g., boiler modules) of the HRSG, and then to outlet components (e.g., steam headers, steam outlet manifold) of the HRSG which may be at reduced or pre-start temperature (e.g., room temperature) that are significantly lower than the temperature of the high temperature steam. As a result of the exposure to the high temperature steam, the portions and/or components of the HRSG may undergo a rapid temperature change. The rapid temperature change may increase the high stress and/or thermal fatigue experienced by the components exposed to the high temperature steam during the start-up procedure. Once the power system is operational for a predetermined amount of time, the steam-exposed components of the HRSG may be consistently heated to an operational temperature, which in turn may reduce the stress and thermal fatigue experienced by the components.
Additionally, when the power plant is shut down again (e.g., not operational), the temperature of the components of the HRSG may again decrease to the pre-start temperature, and upon the next start-up procedure, may experience the same high stress and/or thermal fatigue. In cases of continued exposure to high stress and/or thermal fatigue, components of the HRSG may degrade and/or become damaged, which may reduce operational performance of the power system. Additionally, any damaged components may eventually need to be replaced, which requires the power system to be completely shut down while the damaged components are replaced. The necessity to replace the damaged parts within the power system may reduce the operational time of the power system, which reduces the overall power or load output, and also increases the maintenance costs (e.g., component replacement) for the power system over the operational life of the system.